Add lava to creative inventory (hmm, we're shortly running out of creative inventory space)

src/content_craft.cpp

@@ -486,6 +486,7 @@ void craft_set_creative_inventory(Player *player)
 		CONTENT_CHEST,
 		CONTENT_FURNACE,
 		CONTENT_SIGN_WALL,
+		CONTENT_LAVASOURCE,
 		CONTENT_IGNORE
 	};